<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>212-边界控制.html</title>
</head>
<body>
	
</body>
<script>
	var str = "hava a good day"
	var reg = /\bis\b/g;
	var reg1 = /\Bis/g;
	console.log(str);
	console.log(str.replace(reg,"*"));
	console.log(str.replace(reg1,"*"));
</script>
</html>